In current wireless communication systems, a user equipment (UE) communicates with a network node (such as a base station, eNB, or other network device) to receive data over one or more downlink channels in a cell associated with the network node. To maintain channel and data transfer integrity, the UE may likewise transmit control signaling to the network node on one or more uplink channels. For instance, uplink control signaling from the UE to the network node can include hybrid automatic repeat request (HARQ or H-ARQ) acknowledgements for received downlink data, UE reports related to the downlink channel conditions that are used as assistance for the downlink scheduling, and/or scheduling requests indicating that the UE requires uplink resources for uplink data transmissions.
This uplink control signaling can be transmitted, for example, on a Physical Uplink Control Channel (PUCCH), which presently adheres to a multi-segment subframe structure according to which uplink control signal transmissions are scheduled by a network node in the time and frequency domains. Specifically, a typical Long-Term Evolution (LTE) subframe is 1 ms in length and contains two 0.5 ms slots each having a number (e.g., six or seven) of symbols. A number of resource elements corresponding to the available system bandwidth are allocated by a network-side scheduler to one or more UEs in a cell for uplink control transmission during the subframe.
In some subframes, one or more resource elements in a final symbol of the subframe (in the second slot) is reserved for UE transmission of a sounding reference signal (SRS), which is received by the network node and processed to determine characteristics (e.g., channel quality, interference, etc.) of the uplink control channel. In some instances, the UEs may be configured to perform frequency hopping for Sounding Reference Signal (SRS) transmissions. When such switching occurs, a delay in SRS transmission may occur as a result of a signal amplifier adjusting a power level from a first power level associated with PUCCH transmissions to a second power level associated with SRS transmission. In some cases, this delay does not affect control signal transmission or overall performance in the cell. Where, however, the delay reaches a threshold duration (e.g., ˜symbol duration), the SRS may be delayed enough so as to overlap in time and frequency with scheduled PUCCH transmissions in the cell, causing signal “collision.” To avoid this scenario, which introduces interference that can render one or both of the SRS and PUCCH undiscernible by the receiver, one or more subsequent slots may be cancelled, or “dropped,” resulting in wasted system resources and decreased system throughput.
Thus, improved uplink control frame structures and related techniques for uplink signal scheduling are needed to improve system performance in situations where signal collision occurs or may occur.